# What does a "mole" signify? How does the molar quantity relate to the molar mass of carbon dioxide?

Jun 11, 2016

One mole of substance specifies $\text{Avogadro's Number, } {N}_{A}$ of individual particles of that substance.

${N}_{A} = 6.022 \times {10}^{23} \cdot m o {l}^{-} 1$

#### Explanation:

If I have one mole of carbon dioxide, I have ${N}_{A}$ carbon dioxide molecules, i.e. $6.022 \times {10}^{23}$ $C {O}_{2}$ molecules.

Now ${N}_{A}$ ""^12C atoms, have a mass of $12.0 \cdot g$ precisely. And $2 \times {N}_{A}$ ""^16O atoms, have a mass of $32.0 \cdot g$ precisely. Since mass is always conserved in a chemical reaction, it follows that ${N}_{A}$ $C {O}_{2}$ molecules have a mass of $44.0 \cdot g$. Likewise, I could say that the molar mass of $C {O}_{2}$ is approx. $44.0 \cdot g \cdot m o {l}^{-} 1$. You can do this routinely for all formulae, all you need is access to a Periodic Table, which tells you the molar masses of all elements.

The mole is thus the link between the micro world of atoms and molecules, which we cannot see, to the macro world of grams, and litres, which we as chemists can certainly measure effectively.

Given a mass of substance and its formula we can tell the number of individual particles that constitute that mass. This is worthwhile getting stuck in your head now, because if you can master it, you will succeed in A level chemistry.